A pn junction diode made of silicon (Si) has been widely used. This diode relatively easily achieves a high withstand voltage and a low forward voltage. The diode, unfortunately, has a low switching-speed. Accordingly, as a diode having a higher switching-speed, a Schottky barrier diode (SBD) using silicon carbide as a semiconductor material has begun to be used. A typical SBD has a relatively simple main part as disclosed in, for instance, Japanese Patent Application Laid-Open No. 2002-261295 (Patent Document 1). To be specific, the main part of the SBD includes an substrate, an n-type buffer layer, an n-type drift layer, a Schottky electrode, and an ohmic electrode. The Schottky electrode is disposed on the n-type drift layer as an anode electrode. The ohmic electrode is disposed on the n+ substrate as a cathode electrode.